The present invention relates generally to transmissions and more particularly to an electric continuously variable transmission for improving hybrid vehicle efficiency.
The powertrains of conventional vehicles are designed to provide more power than required for the vehicle at cruising speeds. Specifically, the engine of conventional vehicles is larger than required to provide power for acceleration and hill climbs. This extra power is not required once the vehicle is at cruising speed. As a result, conventional vehicle powertrains are inefficient.
Therefore, it is desirable to have an improved vehicle powertrain for implementation in a vehicle, such as a hybrid vehicle, which overcomes inefficiencies inherent in a conventional powertrain.
Additionally, various types of continuously variable transmissions (CVTs) have been developed throughout the years. The object of a CVT is to provide a continuously variable drive ratio from a transmission enabling an engine to run at an optimum point on a brake specific fuel consumption curve. Essentially, CVTs aim at improving engine efficiency by enabling the engine to continuously run at its most efficient point. Due to the significant complexity, traditional CVTs have posed problems in both implementation and application. Traditional belt drive-type CVTs are also inefficient in that significant parasitic losses occur in achieving continuously variable transmission ratios. Moreover, such devices are power limited.
Therefore, it is desirable in the industry to provide an improved CVT for implementation in a vehicle, such as a hybrid vehicle, which overcomes the deficiencies of traditional CVTs.
In achieving the above identified objectives, the present invention provides an electric continuously variable transmission comprising an input shaft and an output shaft in mechanical communication with first and second planetary splitters. A first electric motor/generator selectively drives the first planetary splitter or generates electrical energy from the first planetary splitter. A second electric motor/generator selectively drives the second planetary splitter or generates electrical energy from the second planetary splitter. A lock-up clutch or brake is in mechanical communication with the first planetary splitter for selectively locking a sun gear of the first planetary splitter. A low range is achieved by feeding electrical energy from the second electric motor/generator to the first electric motor/generator for driving the first planetary splitter. A mid range is achieved by feeding electrical energy from the first electric motor/generator to the second electric motor/generator for driving the second planetary splitter. A high range, or overdrive, is achieved by engaging the brake. Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art.